Trucks, buses, locomotives and transit vehicles typically contain compressed air systems that operate brakes and perform other functions such as opening and closing doors, for example. Air that emerges from air compressors in such systems often contains moisture and lubricating oil mist vaporized within the air. Such moisture and oil mist contaminants must be continuously removed from the compressed gas handling system to prevent failure of the system due to build-up of water or sludge in the compressed air lines.
One problem with such air dryers is that particulate material and soot can easily clog the filters of such apparatus, which sometimes causes the filters to crack or break. When filters break, they lose the ability to filter contaminated air. Moisture (water vapor) is considered a contaminant in such systems, and when a filter breaks, unfiltered contaminated gas is allowed to seep through the break, preventing the dryer from operating effectively. In general, removing oil and moisture from a contaminated stream can be a challenging task.
If water or moisture is allowed to build up inside pneumatic air lines in such apparatus, then it is possible that the brakes will fail or alternatively, air actuated pneumatic mechanical apparatus will stop working. On a subway car or a bus, this could mean that the doors will not open or close properly, or the pneumatic load levelers will stop working properly. Many of the components in modern day buses for example, are air driven. It is therefore extremely important to keep moisture and contaminants out of the pneumatic air lines in such systems. Furthermore, oil is a contaminant which degrades and causes further maintenance problems for such pneumatic systems.
It would therefore be desirable to provide a system, apparatus and method for removing contaminants from pneumatic air lines effectively and efficiently. A method of filtration that is capable of removing both the solid particulates, such as soot, and also the contaminants such as entrained oil and water mist is preferred. Furthermore, a method for removing such contaminants which preserves the integrity of the filtration apparatus, and does not undesirably cause filters to fail, would be highly desirable.
A twin tower gas drying system is shown herein by way of drawings and written description. The invention is capable of several configurations, and a person of skill in the art will recognize that other configurations consistent with this description are possible, and within the scope of the invention.
In the invention, a separation means is employed for removing particulate material from a stream of unpurified gas. Typically, a scrubber pad is used as the separation means, but other means for effecting separation may be employed as well. Additionally, a pre-filtering means is used for removing impurities from said stream of unpurified gas flowing from said separation means. First and second coalescing filters are employed to clean the air, the filters being capable of removing water and oil mist from said stream of unpurified gas flowing from said pre-filtering means. Further, a first tower is provided having a first dessicant material therein for removing water vapor from said stream of unpurified gas received from said first coalescing filter so as to supply a first stream of purified gas therefrom. Furthermore, a second tower having a second dessicant material therein for removing water vapor from said remaining stream of unpurified gas received from the second coalescing filter is provided. Finally, a control means is included for controlling flow of unpurified and purified streams of gases through the drying system so that said drying system is capable of alternately switching between supplying gas to said first tower and supplying gas to the second tower.
In one application of the invention, the drying system includes a control means that operates to supply unpurified gas to the first tower while simultaneously purging moisture from the second tower. Also, depending upon the particular configuration employed, it is also possible to employ control means to supply unpurified gas to the second tower while simultaneously purging moisture from the first dessicant material of said first tower.
In some applications, the separation means is a scrubber pad that is capable of operating in a first mode to entrain particulate material upon its surface, and in a second mode to release entrained material from its surface, such that the entrained material is exhausted from the system. In many applications, the scrubber pad flexes in response to air pressure fluctuations to release entrained particulate material from its surface. Then, the material thus released is flushed from the system.
In some applications, the drying system includes first and second towers with first and second cans loaded with dessicant. The drying system of the first tower comprises a first holding means for containing said first dessicant material within said first can to minimize forces acting against the first can. The drying system of the second tower may comprise a second holding means for containing said second dessicant material within said second can to minimize forces acting against the second can.
In another embodiment of the invention, the apparatus may be adapted for drying a moist air stream. The stream may be dried using a housing and a valve body connected to the housing. Furthermore, a chamber is provided within said valve body. The chamber is adapted for separating moisture from a moist air stream, thereby producing a filtered air stream, the chamber further comprises a pre-filter, a first coalescing filter, and a second coalescing filter. Further, a sump is connected to the chamber. The sump collects and expels separated moisture.
A first tower comprises a dessicant material for removing remaining amounts of moisture from the filtered air stream, thereby producing a substantially dried air stream. Also, a second tower having dessicant material for removing moisture from said filtered air stream is provided.
The apparatus also includes a diverter valve that is provided in operable connection to the valve body for affecting the flow of said air streams, the diverter valve being capable of providing in alternating sequence the filtered air stream to the first and second towers to facilitate the simultaneous movement of air along the dessicant material in said first tower, while air in said second tower is purged from the sump. Then, it is possible to repeat the sequence to facilitate the movement of air along the dessicant material in said second tower while air in said first tower is purged from said sump, with alternating repeating cycles.
The invention also may be characterized as a method for drying a wet gas stream having particulate material therein. In the method, it is possible to provide a particulate-containing wet gas stream. Further, the method includes removing particulate from the wet gas stream, and pre-filtering the wet gas stream. The first and second coalescing filters are capable of removing oil and water mist from the prefiltered gas stream, and the output of the first and second coalescing filters comprises a filtered gas stream. Furthermore, a first tower and a second tower are provided, each tower having dessicant material therein for removing wter vapor from said filtered gas stream so as to supply a first stream of substantially purified dry gas therefrom. In some applications of the invention, it is possible to control the flow of said streams of gases to facilitate switching alternately between supplying the filtered gas stream to said first tower, and supplying the filtered gas stream to said second tower.